1. Field of the Invention
The present invention is related to a method of determining the contact point and the contact of the probe, and more specifically, to a method of determining the contact of the probe with a sample surface in an electron microscope and a method to locate the contact point.
2. Description of Related Art
When using an electron microscope, one must take two measures at the same time in the current technique in order to manipulate the probe for making the probe tip in contact with the sample surface. First, a very thin and sharp probe is chosen to ensure that the ultimate contact point between the probe and the sample surface falls at the tip during the operation. Second, the probe must maintain an appropriate tilt angle while approaching the sample surface during the operation, allowing the user to monitor the position of the probe tip all the time.
However, since the image of the electron microscope cannot provide quantitative information of the perspective depth of field, whether the probe tip contacts with the sample surface during the operation is only determined by observing whether or not the probe tip begins to slide laterally. That is to say, the moment of time for the probe tip to contact with the sample surface cannot be obtained exactly. Thus, when the probe tip slides laterally, it is likely that the probe tip or the sample surface has been deformed or damaged due to the over-contact. In addition, as the probe with an extremely thin and sharp tip must be very expensive and liable to get damaged in usage, the maintenance cost of the conventional electron microscope with maneuverable probes is increased accordingly. Further, since the sample surface tends to be damaged by the probe, the overall cost for a typical measurement is also increased accordingly.